Key performance features required in golf balls include distance, controllability, durability and feel at impact. Balls endowed with these qualities in the highest degree are constantly being sought. A succession of golf balls having multi-piece constructions typically composed of three layers have emerged in recent years. By having the golf ball construction be multilayered, it is possible to combine numerous materials of differing properties, enabling a wide variety of ball designs in which each layer has a particular function to be obtained.
Of these, functional multi-piece solid golf balls having an optimized hardness relationship among the layers encasing the core, such as an intermediate layer and a cover (outermost layer), are widely used. For example, golf balls which have three or more layers, including at least a core, an intermediate layer and a cover, and which are focused on design attributes such as the core diameter, the intermediate layer and cover thicknesses, the deflection of the core under specific loading and the hardnesses of the respective layers, are disclosed in the following patent publications: JP-A H11-151320, JP-A 2003-190331, JP-A 2006-289065, JP-A 2011-115593, JP-A H8-336617, JP-A 2006-230661, JP-A 2017-46930, JP-A 2017-86579, JP-A 2009-95358, JP-A 2016-101256, JP-A 2013-150770, JP-A 2013-150771, JP-A 2012-139337, JP-A 2012-80923, JP-A 2012-139401, JP-A 2012-223286 and JP-A H11-206920.
In the golf balls of JP-A H11-151320, JP-A 2003-190331, JP-A 2006-289065, JP-A 2011-115593, JP-A H8-336617, JP-A 2006-230661, JP-A 2017-46930, JP-A 2017-86579, JP-A 2009-95358 and JP-A 2016-101256, the core is formed as a two-layer core, but these two-layer cores lack optimized hardness profiles, leaving room for improvement. In the golf balls of JP-A 2013-150770, JP-A 2013-150771, JP-A 2012-139337, JP-A 2012-80923, JP-A 2012-139401 and JP-A 2012-223286, the core is formed as a two-layer core, but the inner core layer in these two-layer cores has a small diameter. The golf ball of JP-A H11-206920 is a three-piece solid golf ball in which a two-layer core is encased by one cover layer; that is, the cover consists of a single layer. From the standpoint of achieving a greater flight performance and imparting higher controllability on approach shots, there remains room for improvement in the construction of these prior-art golf balls.